I wouldn't bother with that prescription. I did a lot of swimming as a child and it was only once my prescription reached -3/-4ish that I felt the need for correction in the pool. Briefly had a pair of prescription goggles but then I got contact lenses and so wore those with normal goggles.
Pools aren't visually very complex environments for the most part. Provided you can judge how far away the end is when you're close to it and see the outlines of other swimmers, you're OK.