How to beat 3 and 15s
1. ) Never cast any summon unless you have a turtle, and never cast a summon before a turtle.
2. ) do not cast ANY summon (including a turtle) unless you have 2 or more available summons. Sending a turtle out alone will only get him wiped, he isn't a pawn, he's a very crucial force wall for your summons. Alternatively you could hold the turtle in your aura range by allowing the monsters to get near paladog, this creates a damn near permanent tank while you spam casts and summons
3. Hold onto all aoe spells. If your summons have reasonable control of the center, don't waste meteors or bolts, i generally hold onto about 6 of them. So i have room to control summon queues.
Treat Rhinos the same way.
Without a turtle or rhino for the first 20 seconds is an almost a guaranteed lose.