Well it is possible if you change the source code and build.
Before: Brisk Menu 0.4.something (default in 17.10)
After: Brisk Menu 0.5 with small changes to make Icons bigger.
Note that some widgets use built-in Gtk stock icon sizes.
[code]Built-in stock icon sizes.
Members
GTK_ICON_SIZE_INVALID
Invalid size.
GTK_ICON_SIZE_MENU
Size appropriate for menus (16px).
GTK_ICON_SIZE_SMALL_TOOLBAR
Size appropriate for small toolbars (16px).
GTK_ICON_SIZE_LARGE_TOOLBAR
Size appropriate for large toolbars (24px)
GTK_ICON_SIZE_BUTTON
Size appropriate for buttons (16px)
GTK_ICON_SIZE_DND
Size appropriate for drag and drop (32px)
GTK_ICON_SIZE_DIALOG
Size appropriate for dialogs (48px)
[/code]