Android packages not recognized by vs2015

Good day. please for sometimes now I've been having problem running and debugging Android application?using visual studio 2015. Am new to xamarin.form and Android app development, late last year I have access to wireless network so I installed vs2015 and on starting a new Android project, i vs2015 downloaded and installed xamarin whatever needed to run Android app. Some months ago, something happened to my system, so I have reinstall my vs2015 from the offline copy I got then using '--layout' but all updates and xamarin and all packages are gone. so since then I've been struggling with it, I uses metered network now, if I choose vs2015 change/modify from the control panel, by the time I select Android and it's sdk it will show me something around 10 to 15Gb. so, I started downloading it little by little using xamarin sdk manager. The real problem is that after extracting/unzipping those downloaded Android APIs to the Android folder in my C:/program file where the Android sdk and ndk is, vs2015 will show errors among which is 'one of the following packages must be installed' (that's just my words, not exactly how the error was shown. am not on my system right now). vs2015 recognize the folder, the sdk and the ndk. please what can I do?