I open links via context menu item Open in background but background pages begin to load only when tab is selected.
Is it possible to force Google Chrome for Android to load pages which are opened in background?
No, it's not possible, because it makes a little sense. Chrome is a multi-process browser and it uses dedicated processes (in Android terms, Services) for rendering pages. On Android, processes working in background are usually aggressively killed by the system in order to free memory for foreground processes. It makes no sense to do loading of background pages as a renderer in background will most likely be killed soon, it will be just a waste of network and CPU resources. So Chrome just creates a placeholders for background tabs and only "fills" them when the user switches to them.