That would be fine to start with, but eventually the gecko is going to want more space, and more vertical space. You'll need to either get a mesh topper like sleepygeckos has mentioned on here in the past (www.herpsupplies.com/product.cfm?id=SSR40010) (but find one sized for your 15 gallon) or go to a larger and more vertically oriented terrarium.
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear