my guess would be that this transaction is a payment of some sort that you forgot about. some kind of service (faucet, micorjob,...) that you signed up with your bitcoin address and forgot about.

i can't be sure about this being a spam. because the amounts are not the same. otherwise they would all be the same payment amount. and the fee is very large for this type of spam. 151.583 sat/B is not what they usually choose, specially now that 10 s/B is more than enough.