2000 accord lx 4 cyl tires
 

standard tires are 195/65R15; I have a set of 215/65R15's in good shape I'd like to put on. OK or bad idea?

Nope, bad idea, your speedometer and odometer will both register rather low (i.e. you'll be travelling faster and going further than your instruments read) and the new tires may not clear your fenders at full steering lock when on a bumpy road (and may well not clear your rear fenders on a bumpy road as well).

It's hit-or-miss. 98-02 Accords with V6 came stock with bigger tires, but I don't think they were quite THAT big (overall diameter anyway).

If you want to risk the cost of installation (mounting onto the rims), then try & see. But I wouldn't be too surprised if they rub a little.

As well as what Shipo said about the speedometer...