The TZ Series 3/4/5/50 was introduced in 2007 and 2008.
The TZ3/4 wereentryy level cameras and do not have any HD video capabilities.
The TZ5 & 50 have identical specifications and have only 1280x720 HD video capabilities.
The TZ50 has Wi-Fi capabilities
The ZS15 is a new model that has HD video 1920x1080 capabilities.
It also contains many features that were not available in 2008.
I just noticed that the ZS15 also has the important manual controls.
That gives you growing room if you decide to get further involved with photography.
To me it looks like the ZS cameras are the replacements for the TZ series of cameras.