문법 질문: 주어와 동사 수일치가 궁금해요

문장에 나온 밑줄 부분이 맞는지 궁금해요.
“Over the past 12 to 15 years, the amount and types available on the Internet and, in particular, the speed at which we can process the data, have increased to the extent that few people could have imagined.”
틀린 부분이 있다면 어떻게 고치면 될까요?