M215 is the name of a mutation on the Y chromosome.
The YCC website's nomenclature page listed as per 2002 as follows...
|Mutation Name||Region/STS||Size (bp)||Site||mutation||Forward Primer||Reverse Primer||reference|
|M215||UTY1 exon 14||386||163||A->G||gtaaaactcagatatatacatcccatg||aaaaaaaaagaatcactatcttaacg||Underhill et al. 2001|
Nearly all men which are positive for M215, are also positive for M35.
For this reason, the haplogroup names E-M215 and M-35 are often treated as equivalent, and are even sometimes referred to as the "M35/M215" sub-clade (e.g. Underhill et al. 2001).
For further information, see the E-M35 article.