I am Russian nationality and I understand that I do not need visa to enter Vietnam if stay in Vietnam less than 15 days. However, I am planning to travel to Vietnam in December this year, and I will be crossing border and entering Vietnam by bus coming from Cambodia (via Bavet cross border point). Will it be OK for me to cross border and enter Vietnam at that customs point coming from Cambodia without any visa issue?
No worries, there is no problem at all. You can enter Vietnam at any border gates without a visa (airport, borders or sea ports) as long as you stay in Vietnam for less than 15 days.
We hope that helps.