Maximum difference is typically 3% in the overall tire diameter. 205/65R15 = 25.49". Suggested alternatives include: 215/60R15 (-1.31%), 215/65R15 (+2.01%), 195/65R15 (-2.01%), 195/70R15 (+1.00%). For winter tires, a slightly narrower tire like a 195 is often recommended.
Not sure why you need alternate tire sizes as 205/65R15 are fairly common....lotsa brands are available.
Dave