Armour fell out of favour in the 1400s largely because it was ineffectual against the primitive firearms of the day. Whatever rule set you're using, the armour should provide protection against swords but not pistols.
...and the ship's medic will be a whole order of magnitude more effective at treating wounds and diseases than anyone else on world - even with a limited kit.
It will depend on how they play it and how they integrate with the locals, rather than what they have.
Armour fell out of favour in the 1400s largely because it was ineffectual against the primitive firearms of the day. Whatever rule set you're using, the armour should provide protection against swords but not pistols.
I would suggest that you read Oman's Art of War in the Sixteenth Century before making such a blanket statement such as that. Armor, to include full plate armor was still in use past 1600.
Breast and back up through the 1750's.
My success as a physician had gained me many friends, as I studiously avoided the acceptance of any present in return for my services, which I wished them to receive as simple acts of kindness; thus I had placed the Sheik Hassan bel Kader under an obligation, by curing him of a fever; and as he chanced to combine in his own person the titles of both sheik and faky, I had acquired a great ascendency in the village, as my medicines had proved more efficacious than the talismans. "Physician, cure thyself," applied to the Faky, who found three grains of my tartar emetic more powerful than a whole chapter of the Koran.
We frequently had medical discussions, and the contents of my large medicine-chest were examined with wonder by a curious crowd; the simple effect of mixing a seidlitz powder was a source of astonishment; but a few drops of sulphuric acid upon a piece of strong cotton cloth which it destroyed immediately, was a miracle that invested the medicine-chest with a specific character for all diseases.
If not exactly a cure of their Mahometan souls, they acknowledged that I held the key to their bowels, which were entirely dependent upon my will, when the crowd of applicants daily thronged my medicine chest, and I dispensed jalap, calomel, opium, and tartar emetic. Upon one occasion a woman brought me a child of about fifteen months old, with a broken thigh; she had fallen asleep upon her camel, and had allowed the child to fall from her arms. I set the thigh, and secured it with gum bandages, as the mimosas afforded the requisite material. About twenty yards of old linen in bandages three inches broad, soaked in thick gum-water, will form the best of splints when it becomes dry and hard, which in that climate it will do in about an hour. There was one complaint that I was obliged to leave entirely in the hands of the Arabs, this was called "frendeet;" it was almost the certain effect of drinking the water that in the rainy season is accumulated in pools upon the surface of the rich table lands, especially between the Atbara and Katariff; the latter is a market-town about sixty miles from Wat el Negur, on the west bank of the river. Frendeet commences with a swelling of one of the limbs, generally accompanied with intense pain; this is caused by a worm of several feet in length, but no thicker than pack-thread. The Arab cure is to plaster the limb with cow-dung, which is their common application for almost all complaints. They then proceed to make what they term "doors," through which the worm will be able to escape; but, should it not be able to find one exit, they make a great number by the pleasant and simple operation of pricking the skin in many places with a red-hot lance. In about a week after these means of escape are provided, one of the wounds will inflame, and assume the character of a small boil, from which the head of the worm will issue. This is then seized, and fastened either to a small reed or piece of wood, which is daily and most gently wound round, until, in the course of about a week, the entire worm will be extracted, unless broken during the operation, in which case severe inflammation will ensue.
With respect to advanced medical knowledge and supplies on a low-Tech Level planet, I came across this in the book by Sir Samuel Baker about his travels in Abyssinia in 1861. It clearly gives some idea of what the reaction might be, and how to go about doing so without problems. These are two longer sections, but comments are scattered throughout the text.
Baker as a Physician-Abyssinia
Note: The parasite worm described is the Guinea Worm, and Baker was correct that the source was the drinking water.
You might be right about Baker being better able to cope with a low-Tech civilization than someone of Tech Level 15. Against that, not all planets are that level, and a medic used to a more frontier area, where a lot of the high-Tech level things are not available, might be able to manage to a degree.
Sorry, I should have said that armour fell out of favour after the 1400s not in the 1400s. Except for increasingly ceremonial purposes and occasional attempts to update it with impossibly heavy plates. Modern materials are currently giving it a (temporary?) resurgence. Nevertheless, the point I was helpfully trying to make is still valid: Mediaeval armour will not stop a modern bullet, but is moderately effective against a sword. The rules you choose for weapons and armour should reflect that.
However, the second point I was making also remains valid: A crash landing that is mild enough for the crew to survive is unlikely to destroy stocks of engineering and medical supplies and equipment, most of which are considerably more damage resistant than the human body. Normal and cannibal stocks will last a very long time, more than long enough for someone to notice the ship is missing and organise a search and rescue.