At $15,000 you are talking an older w124. Search for all the links on the 300e sedan (AC, evaporator, m103 valve guides, m104 head gaskets, OVP, worn ball joints, rear thrust and torque arms, complete records and good PPI report, etc.) For the TE, add the rear self leveling suspension bits. Also, they are often called a little 'boomy' on interior noise relative to the sedan. For the CE, the shoulder harness arm can be an issue. Any used car in the $15k range has potential repair issues, and MBs are no exception.
The 300E put on weight as the design aged (don't we all!). This link talks about relative performance of the various I6 engines and model years: 300E Performance Throughout the Years and Comparisons
If you want to approach the nimble character of your 190 16V, read up on ke6dcj posts in the archives and see how he made a killer TE for handling and acceleration. Michael and Glen should also have some tips in the archives - I believe they all 3 own wagons and 500Es, (Glen also has a 16V) and do track events.
For the CE, you will be paying more for that great looking body (Big Surprise!), and may not be able to find the cleanest example for $15k. You will get more bang for your buck on the TE, but don't rule out the early sedans for their value and upgrade potential- buy a clean one for $10-12 and replace the aging suspension bits with the Sportline suspension kit from this site, maybe some nice wheels and tires, possibly a decent stereo.
Maybe I can convince Glen to drive my early sportline sedan and write up a handling comparison to his 500E and his tricked out 16V
Good luck on your car quest!