Not need to even worry about the total number of rows stored across all your tables, performance is a function of the tables included in a particular query, the quality of the query and the quality of the indexing strategy.
Having said that, a 1.6 million rows table - as stated the largest one - is a tiny table.
Point here is, how are queries hitting those tables? what answers the users want?
If user requirements translate in accessing large tables by index then the number of rows stored in such table is rarely a factor affecting performance.
Do user queries require to read the whole 1.6 million rows on your table?
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Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.