By Bethany Wales Vodafone and Three will have to wait longer before finding out if a £15bn planned merger has the seal of approval from the UK’s competition regulator. The Competition and Markets Authority (CMA) said it had extended the period of time it needs to investigate the deal. The plans to combine have been under scrutiny since being announced last summer, delaying what would create the UK’s largest mobile phone network. The two mobile firms say the deal will allow them to invest more in their services and better compete with major rivals, EE operator BT and Virgin Media-O2. In an upda…