The difference should be minimal so I wouldn't worry about it. You can always guesstimate by placing the your stock wheel and tire next to your new rims and tire and see if there is to much of a height difference between them. Also, any decent shop will tell you if you need to adjust you odometer when you get the new rims.

Here is a handy cut and pasted guide from www.whalentire.com

STOCK TIRE SIZE: 195/65R15

Recommended Plus Sizes

PLUS 0 SIZE(S)
195/65R15 Same diameter as stock

185/65R15 0.51 Inches shorter than stock tire


PLUS 1 SIZE(S)
Require 16 inch wheels
205/55R16 0.10 Inches shorter than stock tire

225/50R16 0.12 Inches shorter than stock tire

215/50R16 0.52 Inches shorter than stock tire


PLUS 2 SIZE(S)
Require 17 inch wheels
225/45R17 0.01 Inches shorter than stock tire

215/45R17 0.36 Inches shorter than stock tire

215/50R17 0.48 Inches taller than stock tire


PLUS 3 SIZE(S)
Require 18 inch wheels
225/40R18 0.11 Inches taller than stock tire

215/40R18 0.21 Inches shorter than stock tire

*Note the the stock tire size for a 99 Accord LX is 195/65/R15

As you can see, the differences are very small. Shorter means that the speedo will run a but faster than you are actually going, but not by much, and vice versa. I went from 195/65/R15 to 225/45/R17, they are exactly the same overall diameter and I didn't change my speedo.

Hope that helps.