The coin count itself does not really matter. Each 'coin', or unspent transaction out, has value represented in 64 bits. Whether it is 100 coins or 1 million coins, it will occupy the same 64 bits, the only difference is where the 0's and 1's are placed.
The amount of blocks and the algorithm are really the biggest determining factors.
Hmm,
So in your Opinion would an Algo switch to say X15 or groestl decrease the memory usage , or would a chain swap be required to see the full benefit of such a switch in Algo.
Hmm I don't know why you would choose x15 to decrease resources, I mean it is using 15 different hashing algos so it would be pretty intensive. Not sure about groestls footprint. I do know that both sha256 and blake are both very light weight. Scrypt not as light weight.
The algorithm really only slows you down when you are either syncing the chain, or checking a block that has just been added to the network. The issue is almost entirely with the size of the chain and the fact that there are several things indexed for each block that are stored in memory.