There are several actions in MJ installer that takes most of installation time:
1. Unpacking of MJ archive (MJ consists of about 500 files).
2. Install of MJ core and several additional extensions (plugins, modules, templates). MJ has 4 modules, 5 plugins, and 4 templates, so it takes about 14 times more time to install (with respect to other extensions).
3. MJ tries to unpack bzip2-compressed terawurfl database, and if it's impossible (server has no bzip2 support), the database will be downloaded from mobilejoomla.com.
To skip action#1 from above list you can unpack MJ manually and use "Install from directory" method.
To speedup last action you can download
www.mobilejoomla.com/tera_dump.sql and put it to site root.