How to create a Music Mix video with kdenlive?

I am trying to use kdenlive (0.9.10) on Ubuntu 14.04 to create a simple music-mix clip (for youtube). This clip has a total length of about 90 minutes and is composed of several mp3 tracks, which sometimes slightly overlap. In addition, I have static images which do not overlap. The whole music mix clip does not have any actual moving images in it. To render this project I have chosen the HDEV 720p PAL profile, which is supposed to 'render fast' (according to a youtube video whose source I cannot find at the moment). I started rendering and it gave me an estimated time of about 25 minutes. However, this was 6 (six!) hours ago. Now kdenlive states the estimated time to be about 12 seconds, but this already for hours! I can see the output file building (a m2t file) which grows about 12 kB (i.e. 12000 Bytes!) every second. The current size is about 200 MB. How can I render this video clip faster? I am doing something fundamental wrong? Why is this video clip (which does not even contain 'video') taking such an incredible long time? Maybe there are ways to make it differently? If there is a better tool, I will try this instead!