Private VPN compression for faster Internet

### Background: I'm a student, and currently the Wi-Fi connection at my school is very slow (dead slow). I have an 8Gb 4G data-plan, but even with that, I'm running short at the end of the month. I have set up a Debian headless at home (which has a 400 Mbps connection), and I'm already using it as an automated Seedbox, an L2TP-IPSec VPN, a BTSync server, and an Apache server. I started building two months ago — knowing I wouldn't get blazing fast internet connection — so I'm rather new to Debian ### Here is my question: Is it possible to **efficiently compress data over a private VPN**? I know some iPhone and Android apps like [Onavo Extend](http://www.onavo.com/apps/iphone_extend) can achieve that, and I was wondering how I could put this kind of system in place (if it is indeed effective enough) so that my 4G-data usage would be lighter. If I ever come to installing/building such VPN, it should be compatible with: * Debian (the server), * Mac OS (my computer), * and iOS (my phone). If you have any other suggestion on how I could speed up my school's WiFi. I did some tests on it; ping www.google.com times out, arp -a takes a long time, but eventually displays a few peers, and any speedtest (when the bad connection gives me Internet access) return 0.28 Mbps Down-Speeds.