I am going to buy some temperature Sensors can someone help me out

what temp should the lamp be turn off at? and when should the fans turn be on

I've looked into the snap-disk thermostats for my first projector. The problem with them is that they have much too large a differential. What this means is that the temperatures at which the switch...uh, switches...and resets itself are too far apart. For example, one I was looking at was a normally-open switch that closes at about 95degF. This is good for a cooling fan; however, the differentials are usually around 30degF. This means that the fan will remain on until the inside of the projector is about 65degF--not good. I have yet to find one with a low enough differential.

People here use the attic thermostats that you can buy from Lowe's or Home Depot. I haven't bought one yet, but everyone seems to have good results with them.

If I find anything else out, I'll let you know. I would be interested in a snap-disk thermostat if you can find one that will work well for us (ie. with a very low differential).

What wrong with the fans being on at 65degF??

Nothing is wrong with that, but, if it's a warm or hot season, it's not likely to ever get to that temperature so the fans would continue running without shutting off at all.

It wouldn't work in my home, as it's never at 65 degrees F.
In Winter (northern hemisphere) I keep my heat at 68-70, in summer, my AC is at 73-74.

What if my area temp is 15C would it work?

If the temperature inside the room where the projector is located is that low, yes, that would work.
15C = 59F
I wouldn't want to watch a movie in that temperature