You can find the temperature averages here: http://www.holiday-weather.com/antalya/averages/
It would be reasonable I guess. But it would be better to be there after the end of April for a better temperature. The water will be about 20c in the beginning of May.
Yet, even it is cold, you can find tourists swimming and having sunbath during the winter when it is sunny.
Have a nice holiday, about 5 years ago
You can know the temperature in the Turkey through this website http://www.worldweatheronline.com/Turkey-weather.aspx
And if you want to get explore to the Turkey and you are a new to the Turkey,I suggest you to get the experienced tour operators in Turkey.Similarly here is my suggestion http://www.middaytravelturkey.com/tour-packages/ almost 5 years ago