humm, you should ask someone about egyptians growth rates, thats what you need. I have no clue about how fast they grow but you really should buy a larger tank as soon as you can, 15 gallons isnt very large. I have my leos in ten gallons..I would reccomend getting at least a 40 gallon breeder tank, the 40 gallons are ok also but the breeder tanks are a little wider. Or a tank that is at least 36" long, to provide a good hot and cool side, in a small tank i think that is harder to do, especially with uros who love to bask. Don't get me wrong when i first got my female i had to put her in a 10 gallon tank, because she was very sick and thin. But she didn't move around too much. Once she got better after a week however i moved her into a bigger enclousure and then after about a month i moved her in with my other one. Now she runs aroudn te tank like crazy!
Good luck
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Lauren 
Leos and Uros