We want to import .ecw images. We have done it using QGIS 2.8 for Windows in the past, but we can't using QGIS 2.10 for Ubuntu
No, it is currently not possible to install the GDAL ECW driver on current QGIS and Ubuntu versions in an easy way.
There is an ECW driver in the ubuntugis-unstable repository that works with GDAL 1.10 on Ubuntu 14.04, but needs a hack to make it running under GDAL 1.11: Unable to install ECW support on lubuntu 14.04
Unfortunately, it does not seem to work anymore with newer ubuntu versions. If building GDAL from source is no option for you, I suggest to install a virtual box with ubuntu 14.04 and try my workaround. Or put Windows in the box (if you have a license for that) and just use it for transforming ecw files to Geotiff for further processing.