Based on my experience w/ now 2 yo DD:
(1) 15 mo. olds don't sit still for anything, ever.
(2) He HAS found something that interests him: the mop, broom, and vac! There's no harm in letting him play with those, and it may be a "forbidden fruit" reaction if you let him have toys but NOT those.
(3) At this age, the best toys aren't toys. My DD's favorite things are:
- set of plastic cups (for pouring water back & forth or hiding something under one & then guessing where it is)
- some (too large to swallow) nuts, bolts, & washers DH got out for her
- blankets for making tents or playing peek-a-boo
- rocks for touching, lining up, comparing different ones, etc.
- sand for running through her fingers, pushing one way then another, scooping up & pouring
- DH's and my shoes to put on and "hats" - real or anything that COULD be a hat (plate, book, etc.)
In short, I think you're over-thinking this! Just let him investigate the things he's interested in. Give him a bowl of dry macaroni with a lid on it & let him shake it & turn it over, then when he gets bored with that, take the lid off & let him feel it. Let him push a dustmop around. Once he's satisfied his curiosity about the things HE wants, he may warm right up to the REAL toys you want him to like! :)