Hello I am using Sonar x1 producer I am working on a project. The mix is great I have set all my effects using ozone 5 for mastering. Inside of Sonar everything sounds great however when I mix down the track I am loosing about 15 to 20db of volume.

What soundcard? 
What format are you mixing down to (WAV, MP3)?

I also use Ozone to mix down...I have it in the master bus when I export.  Be careful with the loudness control in Ozone... 

I export and generally get a "not quite as loud as I'd like it" wave.  As long as it's in the 75% or better range when looking at it in your wave editor..... you should be good. 

My fix for that is to normalize it to 98% ...  depending on the highest peak in the song.... that may not give you that much of a volume bump but if the levels are consistent in the song, it can provide a decent  level increase,,,,,some here may disagree, but that's how I do it. As a result the edited wave sounds good, is at a good level and retains it's dynamic range. Using a compressor to bump the levels at this stage can affect the over all mix in a way that you may not like. 

Obviously you have not set Ozones limiter correctly???
If you have Ozone as the last plugin before the signal leaves SONAR, the exported (you are talking about exporting, aren't you?) wav is exactly the level you've set in Ozone.

15-20 dB drop is very, very much though. You must have the mix in Master reasonably hot, around -6 - -3 dB, in order to get a final -1 - -0.3 dB level without having to limit too much (to avoid artefacts).