Considerably means by a large amount. Enough that anybody would notice.
It nearly always sits before a comparative, giving considerably better, considerably more expensive, considerably longer than expected. That is its natural home. The word is formal and it belongs to reports and reviews rather than to conversation, where a lot does the same job. Its usefulness is that it claims a big difference without naming a figure, which is also why careful readers ask for the number.
1adverbconsiderablyBy a large amount.
“The second version is considerably faster.”
From considerable + -ly.
Etymology from Wiktionary, CC BY-SA