Following the instructions (http://first.wpi.edu/FRC/roborio/toolchains/FRCLinuxToolchain2016.txt) for installing the 
build chain on Ubuntu 15.10:

$ sudo apt install frc-toolchain
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 frc-toolchain : Depends: g++-arm-frc-linux-gnueabi (>= 4.9) but it is not going to be installed
                 Recommends: frcmake but it is not going to be installed
E: Unable to correct problems, you have held broken packages.


Digging a few levels deeper shows that at least part of the problem is a dependency on libisl10. Ubuntu 15.10 provides 
libisl13:

$ sudo apt install cpp-4.9-arm-frc-linux-gnueabi
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 cpp-4.9-arm-frc-linux-gnueabi : Depends: libisl10 (>= 0.10) but it is not installable
E: Unable to correct problems, you have held broken packages.