I'm doing a project on water purity finder. I dont know which arduino board can be used for the project. It uses upto 15 sensor modules excluded display, WiFi module. Can you tell me which board is better for my project.
It depends on what kind of sensors you're using. If you use I2C based sensors, and you can configure each with a separate I2C address, you could theoretically drive up to 128 of them. I say theoretically since you might not be able to push the signal across an I2C bus with that many devices on it. You could certainly manage 15 of them however.
The Mega 2560 has tons of I/O lines, so that might be a good choice if you need separate single lines for each sensor.
If you need a separate analog input for each of your sensors, you'd need to use an Arduino with at least 15 separate analog inputs. The Arduino Mega 2560 has 16, so that would work.
If you need 4 bit binary inputs, you'd need 4*15 or 60 inputs. The Mega 2560 has 54 digital inputs, which would not be enough for that situation.
You might also be able to use some sort of signal multiplexer and enable one sensor at a time.
Tell us which type of sensor you're using and we can provide more concrete help.