I largely skipped 1E, but I do know that in Tomb of Horrors, everything is a trap. Everything. And Find Traps won't save you from many of them so beware shmuck-bait. And roll a second character.
I do know that your 8 and your 15 are almost identical in value in 1E and 2E, ability scores meant jack-all in that range. And that 16 isn't much either. Your Constitution should get the 15 or 16, that's 10 or 20 hit points in a system that caps out 10 HD. Though if you go Elf, use the 13 or 14 in Con instead.
Don't forget level caps for Demihumans, Thief is about the only one I think that has a high level cap. So the F/M/T is probably the better long term option. Actually, if Fighter is capped at a low enough level (6?), Mage/Thief may have a better THAC0 than a Fighter/Mage just because the thief xp chart is so favorable.
With your stat swapping you could make a dual classed Human if you wanted. (Those 14s aren't doing anything useful.) There are some interesting things you can do with that when starting at high xp.
If the DM isn't giving you equipment for your level, grab the Armor spell and have the best AC in the party.
I remember grognards talking about shenanigans with Cavalier and its stat growth, but I don't have the book to recall the specifics. If you have it, take a look.
Let us know how long it takes for first deaths.