Confusion between PPA's for Trusty and Willy

I am having libvips issues on my Ubuntu 15.10 machine, related to an image processing library. See https://github.com/jcupitt/libvips/issues/350

One weird thing is that I have two PPAs pointing to libvips:

# michael-heuberger at M1 in ~ [19:18:36]
$ sudo apt-get install libvips
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libvips is a virtual package provided by:
  libvips38 7.40.6-2build2~ubuntu14.04.1~ppa1
  libvips38v5 7.40.6-2ubuntu2
You should explicitly select one to install.

E: Package 'libvips' has no installation candidate

How can I remove this one?
libvips38 7.40.6-2build2~ubuntu14.04.1~ppa1

In all my PPA sources it is not listed. Weird.

The main cause for all of this is that I fail running a node.js app. Always this error is shown:

module.js:460
  return process.dlopen(module, path._makeLong(filename));
                 ^

Error: libIlmImf.so.6: cannot open shared object file: No such file or directory
    at Error (native)
    at Object.Module._extensions..node (module.js:460:18)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)
    at Module.require (module.js:366:17)
    at require (module.js:385:17)
    at Object.<anonymous> (/home/michael-heuberger/binarykitchen/code/videomail.io/node_modules/sharp/index.js:12:13)

Any clues?