Rosa, if you are going to give us a Lotto prayer then I will have to give you some tile advice!!
You say 1.5 grout. Do you mean 1.5mm grout line? That's pretty ambitious for a non tiler (sorry, thats an assumption on my part). Also, are the tiles rectified (i.e. all exactly the same size). Lots of large tiles can vary between 1-2mm in overall size. Even a pro tiler would not use such a small grout line. Go for 3mm and use levelling clips.
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The above is 600x600 tiles and I used a 3mm grout line. Porcelain over underfloor heating.
Good luck.
p.s. Do I buy my lotto ticket for this Fridays draw? !!