Rival,
I don't remember just how long it took me to read the whole Bible, that was over 50 years ago. The one thing I have learned about reading the Bible straight through is, you do not learn very fast, because the subjects in the Bible are not put together in one place, so learning Doctrines is very hard to do that way.
From my experience, learning by Topics, is the best way to learn the truths of the Bible. You need to pick a Topic, and find all the places in the Bible where that topic is mentioned, then meditate on each Scripture, to make sure you understand each one, then put the Scriptures together, and meditate on what they all are teaching. Then form a theory about what you believe, from what you have read. Thein you must test your theory, by making sure that ALL the Scriptures you have found on your Topic agrees with your theory. If all Scriptures do not agree, your theory is wrong, you must form a theory that takes into account what every Scripture says. Remember this point: Scripture explains Scripture!!!
Another thing to remember is, it is not meant to be easy, to understand the Bible, we must search for truth as you would for hid treasure, and you will find it if you are sincere, and pray to God for His Holy Spirit to help you understand the deep things of God, Proverbs 2:1-12, 1Corinthians 2:10. Genesis 40:8, which says; Do not interpretations belong to God? All Scripture is related to all other Scripture, Intertexuality, and all Scripture tells the same story, Univocal, and is true, because the Almighty has promised to protect His word from every generation, Psalms 12:6,7, John 17:17, 1Peter 1:25.