It doesn't matter if the total Amps of the breakers exceeds the Amps of the breaker on the supply. The following rules are important.
1. The breaker protecting the wires should not be larger than the ampacity of the wires.
2. The actual load in use at one time should not exceed the capacity of the wire and breaker supplying the load.
Don't mess with trying to find 7.5 Amp breakers. If you find them they will be expensive.
If you follow Rule 1 you will be safe.
If you follow Rule 2 you will not suffer the inconvenience of tripping breakers.