Similar to what the KOMA-script classes provide, the memoir document class also offers 14pt and 17pt (but not 16pt) options for the basic font size of a document. The memoir class-related files should be installed automatically by most modern TeX distributions. If not, use your package manager -- tlmgr or MikTeX's own update program -- to install them.
You'd select these fontsize options with the commands
\documentclass[14pt]{memoir}
and
\documentclass[17pt,extrafontsizes]{memoir}
respectively. I suggest you include the option extrafontsizes when using the 17pt size option. Doing so will ensure that commands that change relative font sizes -- such as \Large, \huge, and \Huge -- will produce reasonable-looking results. Specifically, the Latin Modern fonts in T1 encoding will be loaded instead of the default Computer Modern fonts in OT1 encoding.