unless this http://oldschool.tools/calculators/melee-max-hit maxhit calc is wrong you get the same maxhit with your stats + 31 pray (65cb) or 84 str + extra hp levels (also 65cb)
so basically getting 31 pray gives you the same maxhit as getting str levels for the same cb lvl and staying 15 pray but obviously you get itemprotect, the 10% att pray (if you can activate it) and it is way quicker to train prayer than strength.
So yeah it is worth it to get prayer over str levels at that point since its easier to train.
Obviously this doesnt apply 100% if you train str without gaining (full) hp exp