how is this possible?

plays more blitz than daily...its not very uncommon on here

Isn't it unusual, most people are good at slow games, because you get more time to think,

not unusual at all...look at the multiple i cant improve threads and note how much blitz and bullet they play...lots of people enjoy blitz more☺

Its an online rating.  It means NOTHING.  

This.

The same happens with my rating.  I have played only one  daily game (which I lost),  but  many thousands of blitz and some thousands of bullet.

In fact I had no intention to start a daily game, I started it accidentally accepting a challenge.

This actually seems pretty common... people who love to play live games, but can't care about games that go on for more than a few days.. they just lose interest?

I have a question, if I improve my slow games will I automatically improve my rapid games? Recently I almost hit 1500 rating in slow games, does it indicate that I can also achieve 1500 rating in rapid games?

The ratings here are not easy to compare - just remember that. 

It might be better to compare yourself to percentile - if you're 90th percentile in one rating, it might be possible to get to 90th percentile in another rating category.