Ahhh yes, thanks for the info about the stock sizes.
Overall tyre diameter.
185/70/14 = 615mm
205/65/14 = 622mm
195/65/15 = 634.5mm
215/65/15 = 661mm
235/45/17 = 643mm
The 215/65/15 is larger than the acceptable 15mm difference in overall diameter and technically contravenes ADR unless you get your speedo recalibrated or change your overall outside tyre diameter. Yes it will throw your speedo out a fair bit.
Go for a wheel/tyre combination similar to stock to maintain speedo accuracy.
The closer you get to the oem figure, the more accurate the speedo will be.
Any excuse to throw on a set of new mags and tyres is a good one!
Here's some info when I was engineering my car:
The overall outside diameter of the wheel and tyre combination must be no more than 15mm over the largest diameter wheel and tyre combination specified for the vehicle and not more than 15mm below the smallest diameter wheel and tyre combination specified for the vehicle.
Manufacturer Overall Outside Diameter measurements as per tyre placards on Lancer Evolution
195/65/15 = 634.5mm 205/60/15 = 627mm 205/55/15 = 605.5mm
Therefore the wheel and tyre combinations allowable under section LS would include, but not be limited to, the following which fall within manufacturer overall diameter specifications:
205/45/16 = 591mm 205/50/16 = 611mm 215/50/16 = 621mm
205/40/17 = 596mm 215/40/17 = 604mm 205/45/17 = 616mm
215/45/17 = 625mm 205/40/18 = 621mm 215/40/18 = 629mm
215/35/18 = 608mm 215/30/19 = 611mm 215/35/19 = 633mm