Just another opinion , Ventura type racks are great . Sure the weight is up high but 15kg when turned around and sitting like a pillion is nothing . I have the large Ventura bag that has the expanding top section and it has been great . There have been no rub marks on the paintwork and never had an issue with worrying about something being loose . Side pockets are easily accessed for small stuff like house keys , phone , wallet etc .
The Ventura bag removes easily when you want to and is great at the supermarket , beats the shit out of those green enviro bags .
I have had way more than 15kg in mine for long trips and know of a certain KSRC chick who takes that amount in just makeup and hair product
Throw over saddle bags suck
And tank bags annoy me when riding with the extra worry of scratching the paint . When you update bikes you can just change the rack , and if you are lucky may have to only get the side rails if the centers are the same . ZZR 250 centers are the same as 01 ZX9 .